Radiation image detector

ABSTRACT

A radiation image detector includes a radiation-image-detector main body and a vacuum container. The radiation-image-detector main body generates charges by irradiation with an electromagnetic wave for recording that carries a radiation image and records the radiation image by accumulating the charges. The vacuum container is sealed to store the radiation-image-detector main body in a vacuum.

This application is a divisional of U.S. application Ser. No.12/180,995, filed Jul. 28, 2008, which claims priority to JP2007-195900, filed Jul. 27, 2007, each of which is incorporated hereinby reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiation image detector thatgenerates charges (electric charges) by irradiation with anelectromagnetic wave for recording, the electromagnetic wave carrying aradiation image, and that records the radiation image by accumulatingthe charges.

2. Description of the Related Art

These days, in the field of radiography using X-rays (radiation) formedical diagnosis or the like, various kinds of X-ray radiographyapparatuses have been proposed and used practically. The X-rayradiography apparatuses use radiation image detectors that includesemiconductors as the main parts thereof and detect X-rays that havepassed through subjects. Accordingly, image signals representing X-rayimages related to the subjects are obtained.

Further, as the radiation image detectors that are used in the X-rayradiography apparatuses, various kinds of radiation image detectors havebeen proposed. For example, if the radiation image detectors areclassified based on the charge generation process for converting X-raysinto charges, there are a radiation image detector using an indirectconversion method, a radiation image detector using a direct conversionmethod and the like. The radiation image detector using the indirectconversion method obtains signal charges by detecting, at aphotoconductive layer, fluorescence output from a phosphor byirradiation with X-rays, temporarily accumulates the signal charges in acharge accumulation portion, converts the accumulated charges into imagesignals and outputs the image signals. The radiation image detectorusing the direct conversion method temporarily accumulates signalcharges that have been generated in a photoconductive layer byirradiation with X-rays in a charge accumulation portion, converts theaccumulated charges into image signals and outputs the image signals.

Meanwhile, if the radiation image detectors are classified based on thecharge readout process for reading out the accumulated charges from theoutside thereof, there are a radiation image detector using an opticalreadout method, a radiation image detector using an electrical readoutmethod, as disclosed in Japanese Unexamined Patent Publication No. 8(1996)-106869, and the like. In the optical readout method, charges areread out from the radiation image detector by irradiating the radiationimage detector with readout light (an electromagnetic wave for readout).In the electrical readout method, charges are read out from theradiation image detector by scan-driving a switching device, such as aTFT (thin film transistor), a CCD (charge coupled device) or a CMOS(complementary metal oxide semiconductor) sensor, connected to thecharge accumulation portion.

Further, the applicant of the priority application of the presentapplication proposed a solid-state detector using an improved directconversion method in U.S. Pat. No. 6,121,620 and the like. Thesolid-state detector using the improved direct conversion method usesthe direct conversion method and the optical readout method. In thesolid-state detector using the improved direct conversion method, aphotoconductive layer for recording, a charge transfer layer and aphotoconductive layer for readout are deposited one on another in thisorder. The photoconductive layer for recording exhibitsphotoconductivity by irradiation with recording light (X-rays,fluorescence generated by irradiation with X-rays or the like). Thecharge transfer layer substantially acts as an insulator with respect tocharges that have the same polarity with the polarity of latent imagecharges. Further, the charge transfer layer substantially acts as aconductor with respect to transfer charges that have a polarity oppositeto the polarity of the latent image charges. The photoconductive layerfor readout exhibits photoconductivity by irradiation with anelectromagnetic wave for readout. In the solid-state detector using theimproved direct conversion method, signal charges (latent image charges)that carry image information are accumulated at the interface (chargeaccumulation portion) between the photoconductive layer for recordingand the charge transfer layer.

Here, the photoconductive layer of the radiation image detector asdescribed above is made of a-Se or the like, for example. When thetemperature exceeds a glass transition temperature, a-Se or the like iscrystallized. Further, when humidity is high, condensation of vaporoccurs, thereby crystallizing a-Se.

SUMMARY OF THE INVENTION

In view of the foregoing circumstances, it is an object of the presentinvention to provide a radiation image detector that is not influencedby a change in temperature or humidity.

A radiation image detector according to the present invention is aradiation image detector comprising:

a radiation-image-detector main body that generates charges byirradiation with an electromagnetic wave for recording, theelectromagnetic wave carrying a radiation image, and that records theradiation image by accumulating the charges; and

a vacuum container that is sealed to store the radiation-image-detectormain body in a vacuum.

Further, in the radiation image detector according to the presentinvention, a support unit for supporting the radiation-image-detectormain body, the support unit being made of a heat insulator, may beprovided on one side of the radiation-image-detector main body that isopposite to an irradiation side thereof, the irradiation side beingirradiated with the electromagnetic wave for recording.

Further, a part of the outer surface or the entire outer surface of thevacuum container may be made of a material that reflects infrared rays.

Further, a readout circuit for reading out an image signal from theradiation-image-detector main body or a drive circuit for driving theradiation-image-detector main body may be provided on the outside of thevacuum container.

Further, the vacuum container may be made of a material that functionsas an electric shield (a shield against an electric field or the like).

Further, the vacuum container may be made of a material that functionsas a magnetic shield (a shield against a magnetic field or the like).

Further, the degree of vacuum in the vacuum container may be greaterthan or equal to 10² Pa and less than or equal to 5×10⁴ Pa.

In the radiation image detector according to the present invention, theradiation-image-detector main body is stored in a vacuum by sealing thecontainer. Therefore, a heat insulation effect can be achieved by thestructure. Hence, it is possible to prevent the temperature of theradiation-image-detector main body from exceeding the glass transitiontemperature of a-Se by an influence of the temperature on the outside ofthe radiation image detector. Further, it is possible to preventcrystallization of a-Se.

Further, since no air (outer air) is present around theradiation-image-detector main body because of the vacuum structure, itis possible to prevent condensation of vapor. Therefore, for example,when the radiation-image-detector main body uses an indirect conversionmethod and CsI:Tl as a wavelength conversion material, it is possible toprevent CsI:Tl from deliquescing. Further, it is possible to preventcrystallization of a-Se. Further, it is possible to prevent breakage ofinsulation caused by condensation of vapor during application of highvoltage.

Further, the sound insulation effect achieved by the vacuum structurecan prevent resonance of the radiation-image-detector main body causedby external disturbance noise. Further, it is possible to preventunevenness (irregularity) in the radiation image that is read out fromthe radiation-image-detector main body.

Further, in the radiation image detector according to the presentembodiment, if a support unit for supporting theradiation-image-detector main body, the support unit being made of aheat insulator, is provided on one side of the radiation-image-detectormain body that is opposite to an irradiation side thereof, theirradiation side being irradiated with the electromagnetic wave forrecording, it is possible to further reduce the influence of the outsidetemperature.

Further, if a part of the outer surface or the entire outer surface ofthe vacuum container is made of a material that reflects infrared rays,it is possible to prevent an increase in temperature caused byirradiation with infrared rays.

Further, if a readout circuit for reading out an image signal from theradiation-image-detector main body or a drive circuit for driving theradiation-image-detector main body is provided on the outside of thevacuum container, it is possible to prevent an increase in thetemperature of the radiation-image-detector main body by heat outputfrom the radiation circuit and the drive circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagram illustrating an embodiment of aradiation image detector according to the present invention;

FIG. 2A is a top view of another embodiment of the radiation imagedetector according to the present invention;

FIG. 2B is a side view of the embodiment of the radiation image detectoraccording to the present invention; and

FIG. 2C is a sectional diagram at line C-C in FIG. 2A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described indetail with reference to the attached drawings. FIG. 1 is across-sectional diagram illustrating the schematic structure of aradiation image detector according to an embodiment of the presentinvention.

A radiation image detector 10 includes a radiation-image-detector mainbody 11 and a vacuum container 12. The radiation-image-detector mainbody 11 generates charges by irradiation with a radiation and records aradiation image by accumulating the charges. The vacuum container 12 issealed to store the radiation-image-detector main body 11 in a vacuum.

The radiation-image-detector main body 11 may be any kind ofradiation-image detector main body as long as theradiation-image-detector main body 11 can generate charges byirradiation with a radiation and record a radiation image byaccumulating the charges. The radiation-image-detector main body may usea direct conversion method. Alternatively, the radiation-image-detectormain body 11 may use an indirect conversion method and include awavelength conversion material, such as CsI:Tl. Further, theradiation-image-detector main body 11 may use an electrical readoutmethod. Alternatively, the radiation-image-detector main body 11 may usean optical readout method. In the present embodiment, theradiation-image-detector main body 11 uses a direct conversion methodand an electrical readout method. Further, in the present embodiment,the radiation-image-detector main body 11 includes a photoconductivelayer made of a-Se.

The vacuum container 12 includes an accommodation portion 13 and a topplate portion 14. The radiation-image-detector main body 11 is housed inthe accommodation portion 13 and the top plate portion 14 is a lid forthe accommodation portion 13. Space enclosed by the accommodationportion 13 and the top plate portion 14 that have been sealed is avacuum. It is desirable that the degree of vacuum in the space isgreater than or equal to 10² Pa and less than or equal to 5×10⁴ Pa.

Further, it is desirable that the accommodation portion 13 is made of amaterial that functions as an electric shield (a shield against anelectric field). For example, it is desirable that the accommodationportion 13 is made of metal. Alternatively, the accommodation portion 13may be made of a material that is produced by coating resin with metal.Alternatively, the accommodation portion 13 may be made of a materialthat functions as a magnetic shield (a shield against a magnetic field).For example, the accommodation portion 13 may be made of a material,such as a permalloy, which has high magnetic permeability, and amaterial called as Permalloy C according to the JIS (Japanese IndustrialStandard). Permalloy C is obtained by adding Mo, Cu, Cr or the like to apermalloy.

The top plate portion 14 is composed of an aluminum vapor-depositioncoating 14 a and a carbon plate 14 b. The aluminum vapor-depositioncoating 14 a reflects infrared rays and the carbon plate 14 b absorbsinfrared rays. Further, the aluminum vapor-deposition coating 14 a andthe carbon plate 14 b are attached in such a manner that the aluminumvapor-deposition coating 14 a is positioned on the outer side of theaccommodation portion 13. Further, it is desirable that parylene coatingis applied to the carbon plate 14 b so that the vacuum in the vacuumcontainer 12 can be maintained.

The radiation-image-detector main body 11 is supported byheat-insulation support units 15, which are made of heat insulationmaterial (heat insulator). The heat-insulation support units 15 areprovided on one side of the radiation-image-detector main body 11 thatis opposite to an irradiation side thereof, the irradiation side beingirradiated with a radiation.

Further, a TCP (Tape Carrier Package) 16 is connected to theradiation-image-detector main body 11. The TCP 16 is drawn out to theoutside of the vacuum container 12 and bent along the outer surface ofthe vacuum container 12. Further, an end of the TCP 16 is connected to aprinted circuit board 17 (a printed substrate, a printed board or thelike) in which a predetermined image processing circuit has beenprovided. The printed circuit board 17 is provided on one side of theradiation-image-detector main body 11 that is opposite to an irradiationside thereof, the irradiation side being irradiated with a radiation.Further, a seal material 19 is provided at a hole portion that has beenformed on the vacuum container 12 to draw out the TCP 16 to the outsideof the vacuum container 12. The seal material 19 is provided to maintainthe degree of vacuum in the vacuum container 12.

Further, an IC chip 18 including a readout circuit (amplifier) and adrive circuit (gate driver) is provided in the TCP 16. The readoutcircuit reads out image signals from the radiation-image-detector mainbody 11 and the drive circuit drives the TFT. The IC chip 18 is providedon the outside of the vacuum container 12.

Further, a heat pipe and a heat radiator 20 are provided for the IC chip18 to make heat that has been generated in the IC chip 18 escape (beoutput) therefrom. Further, a fan 21 is provided to make the heat in theheat radiator 20 escape therefrom. Further, a Peltier device may beprovided to cool the IC chip 18.

Further, a case 22 is provided in such a manner to surround the entireouter surface of the radiation image detector 10.

Further, in the radiation image detector 10 according the aforementionedembodiment, it is desirable that a convex curl is formed on the topplate portion 14 in advance so that when the inside of the vacuumcontainer 12 is vacuumized, the top plate portion 14 does not concavelybend toward the inside of the vacuum container 12.

Further, as illustrated in FIGS. 2A through 2C, ribs 23 may be providedto prevent the top plate portion 14 from being bent toward the inside ofthe vacuum container 12. FIG. 2A is a top view of the radiation imagedetector 10 and FIG. 2B is a side view of the radiation image detector10. Further, FIG. 2C is a sectional diagram at line C-C in FIG. 2A. Itis desirable that the ribs 23 are not formed in an image area in whichthe radiation image is recorded. When the ribs 23 are formed in theimage area, it is desirable that the thickness of the ribs 23 issufficiently thin so that the ribs 23 are not captured in a radiationimage, in other words, so that the ribs 23 do not appear in theradiation image.

1. A radiation image detector comprising: a radiation image detectormain body having a wavelength converting material including CsI, whichgenerates light by being irradiated with radiation that bears aradiation image, that generates charges by being irradiated with lightgenerated by the wavelength converting material, and that records theradiation image by accumulating the charges; the radiation imagedetector main body being sealed in a vacuum.
 2. A radiation imagedetector as defined in claim 1, wherein: one of a readout circuit forreading out an image signal from the radiation image detector main bodyand a drive circuit for driving the radiation image detector main bodyis provided outside the vacuum seal.
 3. A radiation image detector asdefined in claim 2, wherein: the readout circuit is equipped with a heatrelease means, which is at least one of a heat dissipater, a fan, a heatpipe, and a Peltier element.
 4. A radiation image detector as defined inclaim 1, further comprising: a vacuum container for sealing theradiation image detector main body within the vacuum.
 5. A radiationimage detector as defined in claim 4, wherein: at least a portion of theouter surface of the vacuum container is formed by a material thatreflects infrared rays.
 6. A radiation image detector as defined inclaim 4, wherein: the vacuum container is formed by a material thatfunctions as an electrical shield.
 7. A radiation image detector asdefined in claim 4, wherein: the vacuum container is formed by amaterial that functions as a magnetic shield.
 8. A radiation imagedetector as defined in claim 4, wherein: the degree of vacuum in thevacuum container is within a range from 102 Pa to 5 104 Pa.
 9. Aradiation image detector as defined in claim 1, wherein: ribs are formedoutside an image region in which the radiation image is recorded.
 10. Aradiation image detector as defined in claim 1, further comprising: ribswhich are formed at a thickness that will not appear in the radiationimage.
 11. A radiation image detector as defined in claim 1, furthercomprising: a support unit for supporting the radiation image detectormain body; the support unit being formed by a heat insulator andprovided on a side of the radiation image detector main body oppositethe side which is irradiated by the recording electromagnetic waves.